A Deep Energy Retrofit is a whole-building analysis and construction process that uses “integrative design” to achieve much larger energy savings than conventional energy retrofits. Deep Energy Retrofits can be applied to both residential and non-residential (“commercial”) buildings. DER typically results in savings of 30 percent or more, perhaps spread over several years, and may significantly improve the building value. The term is often used interchangeably with “Deep Green Retrofit” and “Deep Retrofit”.